The story takes place in a post-apocalyptic version of Tokyo where food and clothing are scarce and hard to come by and the only place to find such things in quantity is the "Department Store", a gigantic building from long ago, however the store itself is infested with giant and powerful bio-mechanical androids know as Mannequins which used to be part of the store's security system before it malfunctioned and went haywire, causing the Mannequins to become hostile and animalistic, making sure no human can take any of the treasures within the store's walls. The Mannequins have developed not only the ability to hunt, feed and breed like animals but they have also developed an ability to create and grow many store goods from their own body, and the stronger they become the better their creations. Because of their strength and ferocity, few humans dare to approach them, but those who do are known as Wild Merchants and they live to hunt these creatures to satisfy their greed for the stores' riches.